Process for conversion of coal



Sept. 8, 1970 R. HODGSON 3,527,691

PROCESS FOR CONVERSION OF COAL Filed Dec. 31, 1968 HYDROGENATED com. PRODUCTS osson nom ZONE OIL 4 DECOMPOSITION/ABSORPTION HYDROGENATION 6 ZONE ZONE 3 I 5 ASH- Q 2 2 i3 4 SEPARATION ZONE HYDROGEN l 1 4 v lg ADSORBENT/CATALYST RECYCLE 1 a J FIG.|

3s 27 R A 2 FRESH H2 20 SEPARATOR g LCRUs ER ELUTRIATOR REACTOR L43 FIG. 2

INVENTOR:

RUSSELL L. HODGSON HIS ATTORNEY 3,527,691 PROCESS FOR CONVERSION OF COAL Russell L. Hodgson, Houston, Tex., assignor to Shell Oil Company, New York, N.Y., a corporation of Delaware Continuation-impart of application Ser. No. 746,958,

July 23, 1968. This application Dec. 31, 1968, Ser.

Int. Cl. C10g 1/06, 1/08 US. Cl. 208-10 4 Claims ABSTRACT OF THE DISCLOSURE Hydrocracking coal with solid, particulate, sorbent catalyst by grinding coal to have a smaller particle size than the catalyst, slurrying the coal in oil, subjecting the slurry to hydrocracking conditions while in contact with the catalyst, separating gas and liquid products from the solids, subjecting the solids to size separation to remove noncatalyst solids from catalyst solids, and returning catalyst solids into contact with fresh slurry.

CROSS REFERENCE This application is a continuation-in-part of copending US patent application Ser. No. 746,958, filed July 23, 1968 and entitled Process for Conversion of Coal.

BACKGROUND OF THE INVENTION Field of the invention This invention relates to the hydroconversion of coal to liquid products. More particularly it relates to an improved process for efficient conversion of coal to liquid products employing a dual-functioning solid catalytic adsorbent and a novel processing scheme.

Description of the prior art The conversion of coal to liquid products by hydrogenation is an established phenomenon. The basic con version reaction was demonstrated nearly 60 years ago and coal hydrogenation underwent extensive development in Germany prior to World War II. Despite early interest, however, no process was developed which could compete with petroleum as a source of hydrocarbon fuel and liquid products. However, in recent years there has been a renewed interest in coal as a basic raw material source for petroleum-like products. Renewed interest has been stimulated by diminishing resources of crude oil relative to demand, and the development of more complex and sophisticated petroleum refining techniques. Early coal hydrogentation processes required exceedingly high hydrogen pressures, in the range of 5,000l0,000 p.s.i. Technology now available allows the use of more manageable pressures in the range of 2000-4000 p.s.i.

A concise summary of four coal-treating processes now considered for commercial development is found in Chemical and Engineering News, June 12, 1967. In three of these processes, means other than hydrogenation are used for liquification; and the liquid product, which are obtained either by extraction or by pyrolysis, are hydrogenated. None deal with the problem caused by reactive intermediate products which result in residue and char formation. Thus, fairly large amounts of residue and char must be disposed of by coking or similar means to produce additional products. In the fourth proposal direct United States Patent hydrogenation of raw coal is effected in a process utilizing an ebullating bed of catalyst. In this process the coal and catalyst are intimately mixed and the decomposition and hydrogenation reactions take place in the presence of a continuous liquid phase of feed and products. Significant amounts of very heavy liquid products are produced which must be recycled to the hydrogenation zone or disposed of, as for example, by coking. Ash is removed from the reaction zone with the liquid products. A common characteristic of all these processes is the relatively large amount of low value residue and char that is produced, either as refractory residual liquids, extract residue or pyrolysis coke.

A chief contributor to excessive refractory residue production during the decomposition/liquification of coal is the polymerization and consolidation of the highly reactive initial or intermediate decomposition products. This phenomenon arises from the very nature of the coal itself. Coal consists of a combination of carbon and hydrogen, as well as appreciable amounts of other elements, such as oxygen, nitrogen and sulfur. The carbon is primarily combined in condensed ring structures of high molecular weight which are frequently bound directly together in large clusters by carbon, oxygen, and carbonoxygen linkages. When heated to about 400 C. the solid structure begins to disintegrate and as heating continues, chemical rearrangements continue up to a temperature of 1000 C. and higher. The disintegration products are very reactive, and as they are evolved they, together with the remaining solid matter, consolidate and polymerize into coke or char which is extremely refractory to hydrogenation. To overcome this undesirable eflect at least partially, it has been proposed to heat the coal as rapidly as possible in the presence of hydrogen to temperatures above which the products remain predominantly aromatic. Such a process is proposed by Schroeder, US. Pat. 3,030,297 issued April 1962 and Schroeder, US. Pat. 3,152,063 issued October 1964. In the process of these patents, reaction at temperatures below 800 C. is limited to very short times, in the order of about two minutes. In another proposed process, coal is destructively distilled in a flowing stream of hydrogen and the vapor products, including vaporized condensables, are hydrogenated with a solid catalyst. By maintaining these intermediates in the vapor phase, polymerization and consolidation is retarded until the intermediates are stabilized by hydrogenation over a hydrogenation catalyst. Char, non-vaporized residue, and ash, presumably are not passed over the catalyst. This process is disclosed in Huntington, US. Pat. 3,244,615 issued April 1966. While these methods have merit in reducing the difiiculties associated with coal decomposition, they are not wholly satisfactory due, inter alia, to engineering problems of implementation.

I have now found that selectivity of coal hydrogenation/liquification is markedly improved in favor of gaso line and gas oil by immediately adsorbing the reactive intermediate disintegration products on a solid adsorbent as they are evolved. The adsorption arrests polymeriza tion and the absorbed materials can then be hydrogenated and cracked to stable liquid products with minimum production of refractory heavy products. Moreover, my process has the significant advantage of simple and efficient removal of ash and char from the catalyst system without the necessity of deashing the coal prior to direct hydrogenation.

SUMMARY OF THE INVENTION In broad aspect, the process of the invention involves the following steps:

(1) Grinding coal to a certain maximum particle size.

(2) Decomposition of coal at elevated temperatures in the presence of hydrogen and a solid adsorbent, which immediately adsorbs the decomposition intermediates, is carried out in the absence of a continuous liquid phase, and thus prevents secondary reactions.

(3) Hydrogenation and hydrogenative cracking of the intermediates adsorbed on the solid adsorbent to products which desorb from the solid adsorbent.

(4) Separation of the desorbed products from the solid adsorbent.

(5) Separation of ash and char from the adsorbent/ catalyst, a separation made especially easy because of the efiiciency of conversion of the invention and previous adjustment of the particle size of the coal and the absorbent/ catalyst. The coal is ground and classified to a maximum particle size while the catalyst/absorbent is prepared to have a minimum particle size not smaller than the maximum particle size of the coal. Thereby, the catalyst/absorbent in the total dry particulate solid phase resulting from the process can be separated from the char and ash in the particulate solid phase by separating the dry particulate solid phase into a fraction consisting of particles smaller than the minimum catalyst particle size, and a larger particle fraction, the former fraction being char and ash and the latter fraction being catalyst/absorbent.

(6) Recycle of the adsorbent/catalyst together with adsorbed material to step (2) in a continuous circulating-catalyst process.

(7) Introduction of coal into the high-pressure process as a slurry in oil.

The chemical reaction mechanism leading to the improved results of the process of the invention involves several successive steps: initial decomposition of the coal to intermediate products; adsorption of the intermediates on the solid; hydrogenation and cracking of the adsorbed intermediates which desorb as stable, useful products and finally recovery of the desired products.

The foundation upon which the present invention rests is the discovery that the highly reactive intermediates evolved from the decomposition of coal can be prevented from consolidating and polymerizing by immediate adsorption on a solid adsorbent. By immediately adsorbing the intermediates as they are evolved from the decomposing coal, their reactivity with each other is arrested, allowing further reaction to be controlled as desired. The desired reactions are hydrogenation and cracking to useful, stable products. Having arrested the reactivity of the intermediates, they can be hydrogenated under proper cOnditions in the absence of the rapid competitive side reactions leading to refractory polymerization products. Thus the adsorbent with the adsorbed intermediates may be transferred to a subsequent hydrogenation zone. Hydrogenation is, of course, far more efiectively promoted with the aid of a catalyst. To promote hydrogenation, the adsoribent, having the reaction intermediates adsorbed thereon, may be impregnated with a hydrogenation catalystas by vapor-phase deposition of a suitable metaland the hydrogenation effectively catalyzed. It is more convenient and appropriate, however, to have the hydrogenation catalytic component on the adsorbent initially, thus eliminating the need for subsequent impregnation. Thus, it has been found advantageous to use an adsorbent which has composited therewith a suitable hydrogenation catalytic metal or metal compound component.

Rapid adsorption of the initial decomposition products is essential to the success of the process. To accomplish this objective the adsorbent/ catalyst must initially be intimately mixed with the coal and the solid must be capable of adsorbing the decomposition products as they are formed. In order to insure rapid mass transfer of initial decomposition products to the solid, it is especially important that the decomposition/adsorption take place in the absence of a separate continuous liquid phase. The decomposition step in the absence of a separate continuous liquid phase-contrary to the customary practice in prior processes where the coal is fed in a paste with a heavy liquid and hydrogenation carried out in a single multiphase reaction zoneis one of the chief distinguishing features of the present invention. When the coal is fed to this process as a slurry, the oil employed to form the slurry will be one that substantially completely vaporizes at reaction conditions except for that portion which is advantageously adsorbed by the adsorbent/catalyst in order to effect further hydrogenation and cracking, as for example, recycled heavy products.

By the absence of a separate continuous liquid phase, it is meant that at the conditions of the decomposition adsorption step there is not sufficient liquid present to bridge the coal and catalyst particles and thus form a barrier to the immediate adsorption of intermediates. While there may be liquid present, as by addition of some liquid carbonaceous materials to the coal feed and/or recycle of heavy products in the process as well as instantaneously formed liquid decomposition products, the amount of such liquid and the conditions, i.e., temperature, hydrogen content, catalyst/coal ratio, must be maintained so that a continuous phase of liquid is not formed. That such a condition as described can be easily achieved is well known in the petroleum refining art. For example, in catalytic cracking of a heavy petroleum fraction in a fluidized riser reactor at least partially liquid feed is contacted with catalyst to form a catalyst-feed mixture that is in a dry fluidized state. While liquid is present, no separate continuous phase of liquid exists under the conditions applied.

When the entire adsorption-hydrogenation-desorption sequence is carried out in a single well mixed reaction zone (as is the case in other prior art processes) the presence of liquid retards and/or prevents rapid adsorption of the reactive intermediates and allows consolidation and polymerization reactions which produce refractory residues.

Implementation of this invention in a continuous flow process requires the cocurrent flow of the coal, solid adsorbent/catalyst, and coal decomposition and hydrogenated products through the successive steps in the process of the invention. Several special aspects should be noted which serve to distinguish the process overthe prior art and lead to the surprisingly superior results obtained. For this purpose and for more complete understanding of the invention, reference is made to the drawing wherein:

FIG. 1 is a diagrammatic representation of the reaction sequence of a process embodying this invention.

FIG. 2 is a schematic representation of a preferred embodiment of the invention.

Referring to FIG. 1, raw coal is introduced via line 1 with enough oil introduced through line 4 to produce a pumpable slurry and hydrogen introduced through line 2. This mixture is blended with adsorbent/catalyst and passed to decomposition/adsorption zone 10 where, at elevated temperature and pressure, the coal is thermally decomposed to intermediate products which are immediately adsorbed on the solid. Prior to introduction, the coal was ground to a particle size substantially smaller than the size of the particles of adsorbent/catalyst that were used. From zone 10 adsorbent, with intermediate products adsorbed thereon, together with any desorbed products and unadsorbed ash and char pass via line 3 to hydrogenation zone 12. Separation of desorbed products may be effected between zone 10 and zone 12. In zone 12 the adsorbed intermediates are cracked and stabilized by hydrogenation. The hydrogenated intermediate products, adsorbent/catalyst, ash and char pass via line 5 to separation zone 14 where the hydrogenated coal products are desorbed to an equilibrium level and removed via line 6 for further processing. In this specification equilibrium level means an amount which, at a given set of conditions, does not change substantially on continued recycle of adsorbent. The solid particulate phase including adsorbent/catalyst recycle, ash and char pass to separation zone 16 via line 7 where the ash is easily removed by suitable means such as elutriation, centrifugal classification, or screening since the sizing of coal particles initially precludes the presence of ash or char particles in the product from being as large as the catalyst particles. Ash and char are removed via line 8 and the adsorbent/catalyst solid, now relieved of non-equilibrium adsorbed products is recirculated via line 9 to the beginning of the process where it again contacts a fresh charge of coal. It will be understood that the above description is diagrammatic only and the simultaneous reaction and mass transfer steps which actually occur in a practical flowing process cannot be so neatly segregated. However, this represen tation is useful in illustrating the complex sequential reactions which occur in the present novel process.

While the individual steps in the present process may be carried out in separate well mixed zones, backmixing from one stage to the prior stage is undesirable. For example, decomposition in the presence of aseparate continuous liquid phase of hydrogenated liquid products should be avoided.

In the hydrogenation zone, the presence of a substantial liquid phase would lead to similar difliculties, e.g., retarding the transfer of hydrogen to the adsorbed intermediates and retarding the desorption of the hydrogenated products.

In the desorption zone similar considerations apply. The presence of a liquid phase retards desorption and separation. It is a striking feature of the present process that the hydrogenation is so complete that when the separation stage is reached, the solid (adsorbent/catalyst plus ash and char) is dry. Whatever refractory material is produced remains with the solid adsorbent at an equilibrium level and is recycled with the solid through the system. The circulating solid (if chosen to have sufiicient hydrogenation catalytic activity) obtains an equilibrium level of adsorbed material which does not increase with repeated circulation. Because the solid adsorbent/ catalyst is not admixed with a separate liquid phase, separation of ash is greatly facilitated. When the coal charged to the process is sized to be not larger than the catalyst particles, the solid adsorbent/catalyst is easily separated from ash and char by screening, elutriation or centrifugal classification.

Another important aspect of the present invention is the discovery that the kinetics of the decomposition/hydrogenation/desorption reactions of the present process allows the process in one embodiment to be carried out in a unitary reaction zone. Since decomposition and adsorption-An the absence of a continuous liquid phaseis extremely rapid compared to the hydrogenation reaction, it is possible to carry out the former step at the entrance portion of a unitary reactor, the adsorbent/catalyst with adsorbed intermediates moving to a longer residence time zone where hydrogenation takes place without interference from decomposition and adsorption reaction. In other words, in a moving bed unitary reaction zone, coal and catalyst are initially mixed, the coal decomposed and intermediates adsorbed. As the adsorbent/ catalyst moves through the bed the decomposition/adsorption is completed and hydrogenation, cracking and desorption become the dominant reactions in the middle section of the bed. After sufiicient time the major portion of the adsorbed intermediates are hydrogenated and desorbed, leaving at the exit of the reaction zone a physical mixture of adsorbent having some material thereon, desorbed stabilized products, char and ash which was associated with the raw coal. This mixture is substantially dry, the desorbed products being predominantly vaporous at the conditions applied. Thus, the separation into desired products, adsorbent and ash, and char fractions is greatly facilitated.

The process of the invention may be carried out for the conversion of any type of coal, as for example, bituminous, sub-bituminous or lignite coal as well as partially converted coal that has already been subjected to -liquification processing. The coal is preferably ground or pulverized to facilitate transport, decomposition, and separation of solid products. However, the process may suitably be used to convert coal fines and coal or fines which have been agglomerated or pelleted by various means known to the art if the agglomerates have the proper size with respect to the catalyst, or lose their structural integrity during the decomposition process.

The decomposition/adsorption step can be carried out over a wide range of conditions of temperature and pressure. Temperatures in the range of 200 to 600 C. and pressures in the range of 500 to 3000 p.s.i.g. can be used. Generally, temperatures in the range of 400-500 C. and pressures in the range of 1000-2500 p.s.i.g. are suitable. These relatively mild conditions, in themselves, point up a significant advantage of the present process over those previously proposed. While both higher temperatures and pressures may be used, the problems of rapidly achieving higher temperatures and the economic detriment of higher pressures place practical limits on these variables to the ranges given.

The solid adsorbent/catalyst material suitable for the process has certain essential properties. This material must be solid at the reaction conditions and be capable of rapidly adsorbing the intermeidate products of the decomposed coal. This material should also be uniform in size and in particles not smaller than the maximum size of the coal particles charged to the process.

Numerous materials are known to possess the adsorptive capabilities required to accomplish the purpose of the present invention. For example, naturally occurring or synthetic adsorbent inorganic metal oxides such as montmorillonite clays, kieselguhr, silica, alumina, magnesia, boria, titania, zirconia, beryllia and mixtures thereof. Particularly desirable are the high surface area porous oxides such as cogels or coprecipitates of amorphous silica or alumina and crystalline alumino-silicate zeolites, etc.

While many of the adsorbent solids will have some inherent hydrogenative activity, in general such activity is not sufficient to accomplish the desired degree of hydrogenation necessary in the process of the invention. Therefore, catalytic hydrogenation activity is supplied by compositing with the adsorbent a hydrogenation component, preferably a metal hydrogenation component. Suitable for this purpose are various metals, and metal compoundssuch as the oxides and sulfidesknown to the art for their hydrogenation ability. Of course, it is highly desirable that the adsorbent have a porous structure and high surface area and that the hydrogenation component be distributed in a finely divided or molecular state substantially over the effective adsorptive surface of the solid. Especially preferred hydrogenation components for the adsorbent/catalyst solid of the invention are metals and metal compounds-oxides and sulfides of metals selected from Groups VB, VIB, VIIB and VIII of the Periodic Table of Elements and mixtures thereof. The Periodic Table referred to herein may be found in the Handbook of Chemistry and Physics, 39th edition, Chemical Rubber Publishing Company (1957-1958).

While it is not essential that the adsorbent have catalytic cracking activity, such activity is a definite advantage. In order to obtain the desired hydrogenation and cracking of the adsorbed coal decomposition intermediates only catalytic hydrogenation activity is essential, it being possible to thermally crack the products under the proper conditions. However, catalytic cracking ability is desirable. As will be recognized, many of the adsorbent materials enumerated above possess cracking activity.

Cracking activity can also be increased by various means such as acid-treating and incorporation of halogen components into the adsorbent.

Methods of manufacturing the refractory oxide adsorbent material and of incorporating hydrogenative metal or metal compound and acidic promoters on these adsorbent materials are also well known in the art. The catalitic components may, for example, be deposited by impregnation or by ion exchange from a solution followed by treatment with other reagents to cause precipitation or modification by drying and heating or oxidation or other chemical treatments.

Specific examples of suitable materials which have been found to have special utility for the purposes of the invention are Group VIII and/or Group VIB metal oxides and sulfides incorporated on alumina or silica-alumina and Group VIII metals on faujasite-type zeolites, such as palladium on Yzeolite.

Zeolites having had at least a part of the alkali metal content exchanged for hydrogen ions or divalent metal ions have high intrinsic cracking activity and unusually good adsorptive properties and are thus very suitable for the present invention.

The adsorbent/catalyst may be in any of various physical forms, as for example, spheres, pills, extrudates, granules, etc. The size of these particles while not critical for effecting the reactions is an important variable in the effective utilization of specific embodiments. For example, relatively small particles are preferred to achieve effective adsorption, -to facilitate fiuidization and transfer in a moving bed process. The size and density of the solid adsorbent/catalyst is chosen to facilitate easy separation from dry ash and char by elutriation, screening, or centrifugal classification.

In order to facilitate a clearer understanding of the reaction mechanism upon which this invention rests and practice of the invention, the following experiments will be described before discussion of a specific preferred embodiment. These experiments, while illustrative and not intended to be a limitation on the invention, are useful in understanding the criticality of the sequential steps which characterize the invention.

The following experiment-s demonstrate the initial decomposition and adsorption of the decomposition prod nets and serve to illustrate the importance and practicality of this step in the process of the invention.

Dried Illinois No. 6 coal ground to pass through a 200 mesh screen was reacted in a fixed-bed tubular reactor with a charge of adsorbent/catalyst comprising cobalt and molybdenum impregnated on alumina and sized to pass a 42 mesh screen and be held on a 100 mesh screen. Hydrogen was passed through the bed of coal and adsorbent/catalyst which was maintained at about 1500 p.s.i.g. pressure. The sizing of the coal and catalyst provided easy separation of char and ash from the solid by screening. Successive charges of fresh coal were used with the same adsorbent/catalyst. Each charge of coal (10 g. fed in four 2.5 g. portions) was contacted with 10.3 g. of solid, the solid being recovered and used with a succeeding charge.

The results of this experiment and the pertinent operating conditions are given in Table I.

TABLE I Temperature: 400-450 0. Hz Flow: 400 ce./min. at 1,500 p.s.l.

Bun Products, percent wt. MAF Conversion, period, percent wt. Coal Charge No. min. Liquid Residue O Char MAF 4 x 15 36 12 31 69 4 x 15 53 1 24 76 4 x 15 58 3 15 85 4 x 15 59 4 11 89 4 X 15 60 -2 17 83 x 66 7 9 91 X 4 x 20 as 0 4 91 h 450 0. maximum, time counted when reactor reached 400 C.

b The 10.3 g. charge introduced in four portions and reacted for 15 minutes each.

u Residual material remaining on adsorbent.

d Removed with ash.

These results show that stable operation was approached after the catalyst had been used with six times its weight of coal. At this point a slight decrease in space velocity to about 0.75 to allow increased hydrogenation time was employed, and stable equilibrium operation was achieved. After stable operation was achieved, the liquid yield was 68% at a coal conversion of 91% The foregoing results point up two important functions of the solid adsorbent/catalyst. First, it rapidly adsorbs the intermediates which are formed in the initial coal decomposition; and second, it catalyzes the hydrogenation of the adsorbed intermediates. The first function was carried out with coal and catalyst mixtures in the absence of any added liquid solvent or vehicle. The importance of the second function is illustrated by experiments using silica which has no hydrogenation or hydrocracking activity. In the absence of hydrogenation and cracking activity, the intermediates continued to build up on the adsorbent solid (SiO in a form which was not readily removable. This experiment was the same as previously described and after the first 10 g. charge of coal only 13% wt. liquid was produced, the adsorbent contained 29% adsorbed residual liquid. Total conversion was only 60%, leaving 40% of the coal charged as char.

To approximate a continuous process more closely and further illustrate the process of the invention, experiments were made simulating staged operation. The adsorbent/ catalyst which had previously achieved stable operation in the above example and containing about 25% adsorbed material was divided into two equal portions. To one portion was added a charge of fresh coal and the mixture put at the inlet end of a tubular reactor. The other portion was placed at the exit end of the reactor and separated from the first portion by glass wool. After the reaction period, the catalyst at the exit end was screened to remove char and ash and then mixed with fresh coal and placed at the inlet of the reactor. At the same time, the coal and catalyst at the inlet were moved to the exit end of the reactor for the next reaction period. This operation was repeated over and over with the results shown in Table H. In this operation at 450 C. and a H flow of 400 cc./min. at 1500 p.s.i., stable operation was achieved at a coal space velocity of slightly over 1/2. The results are improved over single-stage operation. The coal is essentially completely converted with a liquid yield of about TAB LE II Temperature: 400-450 (3. H2 Flow: 400 cc./min. at 1,500 p.s.i.

1\ Residual material remaining on adsorbent. b Removed with ash. v 7.5 g. coal, total charge.

In one embodiment of the invention, heavy liquid products, or a portion thereof may be recycled and included in the fresh charge of coal. The amount of heavy liquid product recycled should be insuflicient to form a continuous liquid phase at reaction conditions. By recycling the heavier products, even greater overall conversion to light products, as for example, gasoline boiling range material, can be realized. This is demonstrated by three-stage experiments simulating a continuous Process with recycle.

In three-stage process experiments the contents of a tubular reactor (as in the previously described operations) were divided into three sections by glass wool. Coal was mixed with one-third of the adsorbent/ catalyst solid used in previous experiments and placed at the inlet end of the reactor. One-third of the catalyst Was also placed in each of the middle and exit sections of the reactor. The glass wool maintained the integrity of the three separate sections. After the reaction was carried out at temperatures in the range of 400450 C., the reactor was cooled and depressured and the sections removed. The exit section was screened to remove char and ash and then replaced in the reactor as the first or inlet section. The middle section was moved to the bottom of the reactor and the initial inlet section was moved to the middle. This procedure was repeated over and over, thereby simulating a moving bed of adsorbent/catalyst and coal in a cocurrent flow of hydrogen.

Results of this three-stage operation together with pertinent operating conditions with and without added recycle of heavy products are given in the following Table III. In the recycle runs, heavy product obtained from previous runs was added with the coal feed as recycle. It should be pointed out that, even in the absence of added recycle, there is an effective recycle in the form of the adsorbed material on the recycled adsorbent/ catalyst solid. It is interesting to note that in the recycle run the best results were obtained with an adsorbent/ solid which had been used cumulatively with 26 times its weight of coal.

lighter oils employed to prepare a pumpable slurry as a feed stream will vaporize at reaction conditions and are not considered as a liquid phase.

The amount of liquid which can be included depends upon the nature of the liquid, the specific adsorbent used, operating conditionsparticularly catalyst/feed ratio as well as other factors. The maximum amount of liquid includable can be determined by those skilled in the art without experimentation upon consideration of the above factors.

In another embodiment of the invention, the coal charge may be impregnated with a hydrogenation catalyst prior to introduction to the conversion zone. In this case the catalyst-impregnated coal is decomposed more rapidly without adverse etfect on the adsorption and subsequent hydrogenation of the coal products. Various catalysts and methods of impregnation may be used in the embodiment, such as for example, hydrogenative metal salts and sulfides.

This embodiment and the effects of several different adsorption/ catalyst materials is demonstrated by the following experiments.

Powdered Illinois No. 6 coal was impregnated with molybdenum chloride by slurrying the coal with an ether solution of the salt to obtain about 0.1 to 0.2% wt. Mo on the impregnated coal. The catalyst was then sulfided.

Several adsorbent/catalysts were mixed with impregnated coal and tested under the following conditions: 425 C., 1500 p.s.i., H flow of 200 cc./min. for 5 hours (reaction was essentially complete in 2 hours), and 10 g. each of coal and adsorbent/ catalyst. The results are summarized in the following Table V. The product distribution was markedly affected by the choice of adsorbent/ catalyst. Zeolite-based adsorbent/catalysts produced more gasoline-range products than amorphous silica-alumina adsorbent/ catalysts. The increased gasoline range material was accompanied by increased light gas make. With the zeolite catalysts, the importance of a hydrogenation catalyst (i.e., Pd) and the proper level of acidity was 1 Not measured.

It is of particular significance that in the staged operation, heavy refractory products (975 F. plus boiling point) are substantially eliminated, a striking demonstration of the efficiency and critical importance of the process sequence and conditions. Produt boiling range analysis for the one twoand three-stage operation experiments are shown in the following Table IV.

also demonstrated. The differences between the various amorphous catalysts were not marked, although the increased acidity of the silica-alumina supported materials compared to Co/Mo/Al O resulted in slightly more gasoline range material.

TABLE IV Products, percent Wt. MAF llota lqlll 01-03 IBP-400 F. 400-680" F. 680975 F. 975+ F. yield One-stage (Runs 7-8) 18 25 21 4 68 Two-stage (Runs 4-7) 10 22 27 18 4 71 Three-stage with recycle (Run B) 10 30 33 9 0 72 TABLE v In view of the favorable results obtained with recycle productsypemnt it is obvious that some heavy l1qu1d materials can be Wt-MAF included with the coal charge so long as the amount is Catalyst C 0 C. M 5 below that which would result in a continuous liquid S102 22 37 78 phase. Thus heavy petroleum fractions such as petroleum '(fiZ }f 51-j 1'5f residues, pitches, asphaltene fractions, or coal extract or g gggg g3 5? heavy liquid products from coal pyrolysis, extraction or COMO/AWL: I: 34 33 1, Nl/W/F/SlOrAl203 3s 1s 8 liquifaction could be included with the coal charge in Ni/Mo/Flsior A1203 0 32 29 87 place of or m addition to product recycle. Of course,

While the impregnated catalyst improves the rate of and lowers the temperature required for initial conversion, it should be emphasized that this feature is not essential to the novel process of the invention since the decomposition temperature and/or reaction time may be adjusted to achieve substantially complete decomposition without catalyst impregnated on the coal.

DESCRIPTION OF A PREFERRED EMBODIMENT Having demonstrated the chemical efiiciency and feasibility of the process of the invention, a preferred embodiment of the complete process which makes use of and implements the demonstrated mechanism of the process will now be described.

FIG. 2 of the attached drawing is a schematic representation of an embodiment of the process of the invention. This scheme illustrates an elfective means of utilizing the invention and further illustrates the process but is not to be taken as a limitation thereon.

Raw coal is introduced via line to crusher 21 where it is pulverized and screened through a 50 mesh screen to facilitate further processing. The crushed coal passes via line 22 wherein it is mixed with enough oil to form a pumpable slurry from line 23 to the reaction zone 25. Coal, oil, recycle catalyst from line 26 and hydrogen from line 27 are mixed in the mixing zone 28 and enter the reaction zone as an intimate mixture where they pass cocurrently at relatively low velocity through the reactor. Low velocity is desired to prevent gross backmixing of liquid products to the decomposition zone which could produce a separate continuous liquid phase and restrict the required rapid adsorption necessary to achieve the advantages of the invention. The reaction zone is maintained at a temperature of about 450 C., a. pressure of about 1500 p.s.i.g. and a coal space velocity of about 0.5 (weight of coal per weight of catalyst per hour). Hydrogen is introduced via line 27 at a rate equal to about 100 s.c.f. H per lb. of coal. In the reaction zone the coal is decomposed and the intermediate products immediately adsorbed on the adsorbent/catalyst. The adsorbed products are then more slowly hydrogenated and cracked to stable hydrocarbon products in the middle zone an desorbed from the adsorbent/ catalyst leaving residual material on the adsorbent. The reactor efiluent is a physical mixture of hydrogenated products, product gas, excess hydrogen, char, ash, and adsorbent/catalyst having adsorbed thereon heavy liquid products. This efiiuent passes via line 30 to separator 31 where the stabilized hydrocarbon products are separated and pass via line 32 to separator 33. Hydrogen is removed from separator 33 via line 35 and recycled to the reaction zone together with fresh make-up hydrogen from line 36. Stabilized hydrogenated products are removed via line 37 for further separation and refining. From separator 31 the adsorbent/catalyst, char and ash pass via line 38 to elutriator 40 where char and ash are separated from the adsorbent. Elutriation gas enters elutriator 40 via line 41. Elutriation gas may be any suitable or convenient gas stream including synthesis gas, hydrogen, nitrogen or mixtures which contains little or no oxygen. Oxygen-containing gas such as air is to be avoided since its inclusion leads to combustion of the adsorbed materials. The ash and char are removed via line 42. The adsorbent/catalyst, now separated from the ash and char, but containing equilibrium adsorbed heavy liquid is recycled to the reactor zone via line 26 where it is mixed with incoming hydrogen and fresh coal. Makeup catalyst which is sized so that it will not pass a mesh screen is introduced through line 43.

Make-up hydrogen is introduced into the hydrogen recycle via line 36. Pure hydrogen is not required since any suitable hydrogen-containing gas which is predominantly hydrogen can be used. For example, hydrogen-rich gas containing on the order of 70% volume or more hydrogen is adequate and is often available in a petroleum refinery, as for instance, as off-gas from a catalytic reforming process or other hydroprocessing operations. Of course, synthesis hydrogen gas as from steam-hydrocarbon or steam-coal reforming is suitable.

The total amount of hydrogen charged to the process should be such that there is an excess of hydrogen over that consumed in the conversion. A relatively large excess is usually employed to provide a longer catalyst life and to absorb heat liberated by the exothermic reaction. The amount of hydrogen to be employed is within the skill of those practicing the art. In general, the total amount of hydrogen charge will range up to about s.c.f./lb. of coal or more.

Various modifications, depending on the coal charge, the desired products, depth of conversion and other individual requirements will be obvious to those skilled in the art and are included within the intended scope of the present invention. It is also intended that coal or any intermediate decomposition product of coal may be employed as some or all of the charge to this process.

The elutriation process will remove catalyst fines resulting from attrition along with the small ash and char particles, but large, active catalyst particles, those that will not pass a 50 mesh screen, will tend to stay in the process and circulate. For moving bed processes where pressure drop through the catalyst-coal particle bed is to be minimized while coal-catalyst contact is to be encouraged, a coal particle size that will pass a 50 mesh screen should be maintained, while a catalyst/adsorbent particle size that will not pass a 50 mesh screen should be employed. Obviously this preferred particle size range may be modified to adapt the process for the specific properties of the system being processed.

I claim as my invention:

1. A process for hydrotreating coal which comprises:

(a) grinding and classifying coal to produce a coal feed having a maximum particle size,

(b) introducing said coal feed, hydrogen, and adsorbent catalyst into at least one reaction zone at conditions to decompose and hydrogenate coal and containing hydrogen and an adsorbent catalyst having a minimum particle size not smaller than the maximum particle size of the coal feed,

(c) separating the reaction zone efiiuent into products and a dry particulate solid phase,

(d) separating the particulate solid phase into a fraction consisting of particles smaller than the minimum catalyst particle size and a larger particle fraction, and

(e) returning the larger partic e fraction to the reaction zone.

2. The process of claim 1 wherein said coal feed is introduced into the reaction zone as a slurry of coal in oil.

3. The process of claim 1 wherein said coal feed consists of particles that will pass a 50 mesh screen.

4. The process of claim 1 wherein said particulate catalyst consists of particles that will not pass a 50 mesh screen.

References Cited UNITED STATES PATENTS DELBERT E. GANTZ, Primary Examiner V. OKEEFE, Assistant Examiner Waterman 20810 

